Fine particle percolation in a sheared granular bed

We study the percolation velocity, $v_p,$ of a fine spherical particle in a sheared large-particle bed under gravity using discrete element method simulations for large-to-fine particle diameter ratios, $R=d/d_f,$ below and above the free-sifting threshold, $R_t\approx6.5.$ For $R<R_t,$ $v_p$ initially increases with increasing shear rate, $\dot\gamma,$ as shear-driven bed rearrangement reduces fine-particle trapping but then decreases toward zero due to fine-particle excitation for $\dot\gamma\sqrt{d/g}\gtrsim 0.1$. For $R>R_t$, $v_p$ is constant at low $\dot\gamma$ but decreases toward zero at higher shear rates due to fine-particle excitation.